Battery separator



separator may be of Patented Mu. 1c, 1943 2,314,203' BATTERY SEPARATOR Edward Fairclough, Cleveland, Ohio, assigner to Willa-rd Storage Battery Company, Cleveland,

Ohio, a corporation of West Virginia Application August 1, 1941, Serial No. 405,062

s claims. (ci. 13s-149) This invention relates to battery separators and their manufacture, aims to provide an improved battery separator made from tree bark bers.

Another object is toY provide an improved storage battery separator made of matted redwood bark fibers. Y e Y Still another object of this invention is to provide a battery separator made of tree bark fibers and a binder.

A further object of the invention is to provide an improved storage battery separator made of redwood bark bers and a. binder.

Other objects and advantages of the invention will be apparent from the following description and the accompanying drawing in which:

Fig. 1 is a showing a storage battery separator madeof matted tree bark bers; and

Fig. 2is a'view more orless diagrammatic in form and indicating process steps and apparatus used in the manufacture of arator.

In Fig. 1 I show a separator lll for use between the adjacent positive and negative plates of a storage battery and which is in the form of a sheet made of matted tree bark bers. The sizev and thickness suitable which the separator is to be for the battery in the separator l I prefer to used. In making tive view partly in section` my improved sepand as one of itsobjects, y

use bark fibers obtained from trees of the Sequoia group such as the redwood trees because the fibers obtained` from the bark of these trees are relatively long and possess other desirable characteristics, but I may use bers obtained from the bark of various other trees if the bers'are of suitable length. v

In forming the separator the bers are matted together and` pressed into a sheet, and although the'bers do have suilicient adhesive qualities to pe t such separators to be successfully produced without the use of'a binder, I prefer to use a binder to aid in keeping the fibers from falling apart. Any suitable substance may be used as a binder such as latex, hard rubber dust, or asphalt. I nd that a natural asphalt known as gilsonite" forms a very satisfactory binder and that certain resins also make satisfactory binders providing they are acid resistant and do not introduce any undesirable matter into the electrolyte solution. Gilsonite is a variety of natural asphalt found in the Uinta Valley, Utah, and occurring generally as rounded masses solid hydrocarbonl ne lsuch resin is a pine resin known commercially as vinsoL of brilliant `black fibers is -of convenient size, and

binder, of the kind already mentioned, is employed it should be used in a relatively small amount so as not to interfere with or detract from the absorbent qualities of the separator. In some instances it may be desirable to add-jute fibers or other vegetable or mineral iilbers to the tree bark fibers, instead of one of the abovementioned binders, to give the separators initial strength so that they can be handled satisfac torily. a

I have found the fibers obtained from the bark of redwood trees to be especially suitable for making battery separators because they are relatively long bers' which will form a good mat without the use of any binder whatever, particularly after the caustic treatment hereinafter described, and will form an excellent mat with only a limited amount of binder. bark fibers also have a. high lignin content which not only adds to the life of the separator `and makes it resistant to acid but is known to be a desirable substance in a storage battery because it tends to prolong the life of the battery and enables it to maintain a favorable capacity rating.

The redwood bark fibers have a desired resiliency,

contact with the positive plate so as to preventl loosening or shedding of the active material. Another desirable characteristic of the redwood bark that they do not hydrolyze appreciably in acid. Various materials, particularly cellulose, tend to lose their strength and resiliency in acid, but redwood bark bers contain a relatively small amount of cellulose and probably for this reason possess the quality of resisting hydrolysis.

I also find' that battery separators made from redwood bark fibers have a satisfactory low electrical resistance.

In making storage battery separators from redwood bark or other suitable tree bark, the bark is stripped from the tree, chopped into pieces `passed through a. shredding apparatus which liberates the fibers. The shredded material is cleaned as by screening or any other suitable operation to separate the bers from the dust, dirt, and other matter. The shredding and separation of the fibers from the other matter are preferably carried out with the material in a dry or natural state. The bark llbers thus obtained are relatively long and more or less round and crinkly i form.

When a ment in a caustic solution which removes var- /The redwood y ious impurities such as resins, miscellaneous organic material, small amounts of manganese, and various other ingredients that would prove harmful to storage battery plates. In carrying out this treatment, the bark fibers may be placed in a filter vessel or container, which may be cheese-cloth and which retains the fibers and permits the treating liquid to circulate through the mass. While the bers are retained in the filter vessel or container they are subjected to cooking in a 1% or.11/2% caustic solution (so-Y dium hydroxide) at a temperature of about 190 or 200 F. The flbers` are usually left in the caustic solution for a period of one to four hours, although the time of treatment may be greater or less than this, depending upon the character of the fibers, and are then removed and thoroughly washed to get rid of the caustic solution.

` This caustic treatment apparently removes very little, if any, of the cellulose from the fibers, although the treatment may reduce the weight of the fibers by approximately 25% or 30%.

The washed fibers are next placed in a mixer together with a wetting or foaming agent and the desired binding material, if one is to be used. The fibers may be dried before being placed in the mixer or may be placed therein in the wet condition in which they come from the washing operation following the caustic treatment. The wetting agent should be a substance which will wet the fibers individually and will also produce a foam so that the fibers will separate or be held apart and will not remain in lumps or clots. Although various substances can be used for this purpose, those compounds or salts chemically known as soaps and those chemically known as foam producing wetting agents are preferred. An ordinary soap solution can also be used as the wetting agent, but I prefer tol use a commercially available material of the kind which consists of sodium salts of sulphate mono-esters of a mixture of higher fatty alcohols. This wetting agent or sro-called soap solution is preferably a 1% solution a1- though this 'value may be increased or decreased somewhat as circumstances may require.

As stated above, the binder is also placed in the mixer and during the mixing operation the binder becomes thoroughly distributed among the fibers. The binder should be either in a powdered or granular form, and the grains or particles .should not be of a larger size than that corresponding with a mesh screen. Any one of the binders above mentioned may be used, but I prefer to use the natural asphalt known as gilsonite which is insoluble in water. The amount of binder to be used should be relatively small, as mentioned above, so as not t0 decrease the absorbent properties of the matted bers. I find that the use 0f 10% to 20%by weight of the binder gives good results although the amount used can be varied somewhat and tively high temperature to be can be more or less than the percentage men- .is very satisfactory in the the wetting agent or soap solution through the screen by suction. Suitable apparatus for this purpose is represented in Fig. 2 wherein I show box II having a suction pipe I2 connected therewith and a screen I3 extending across the box and supporting a layer I4 of the mixed material. After the wetting agent or soap solution has been thus removed, the material is washed and as much as possible of the wash water removed therefrom.

In Flg. 2 I also show suitable apparatus for carrying out. the washing of the material and the removal of the Wash Water. This apparatus may comprise a box I5 having a suction pipe I6 connected therewith and a, screen Il extending across the box and on which a layer I8 of the'materlal is supported. A pipe I9 having a plurality of discharge openings discharges water onto the material at. a point above the box I5. The water washes the material and removes the soap solution or wetting agent therefrom, and the Wash water is itself removed from the material by the action of the suction in the box I5. The binder being insoluble in the wetting agent and wash water, remains in the material f in a widely distributed condition throughout the fibrous mass.

The material is now transferred to a press such as the press 20 shown in Fig. 2 in which it is subjected to heat and pressure. As the material comes from the washing operation. it is in a more or less matted condition and is still damp orvwet. Instead of placing the mat immediately in the press 20, it can, if desired, be placed on a hot plate while waiting for the pressing operation and during this interval of time some of the liquid would be evaporated from the material so as to shorten the time required for the pressing operation. Instead of using a press, the material might also be subjected tween heated rolls. The pressure which is applied to the material compresses or molds the same into a sheet of a thickness suitable for battery separators. The heat which is applied to the material serves to dry the same by evaporating the moisture therefrom and also serves to soften the binder so that it will adhere to the bers and hold them together. The gilsonite or lnatural asphalt which I have mentioned above as being a satisfactory binder has a relatively high melting point and thus permits a relaused .in the press which expedites the drying of the material. The temperature at which the material is heated should preferably be just below the melting point of the binder so that the binder will be softened but will not actually ow. I nd that a temperature in the neighborhood of 335 or 340 F. pressing and drying operation when gilsonite is used as the binder but -this temperature may be increased or decreased with the use of different binders and as different conditions may require.

Sovfar as I am aware, the feature of incorporating a binder in granular or powdered form in a mass of fibers and pressing'or molding the mass while heated to a temperature which is below the-melting point of the binder but which softens the binder to secure adhesion of the bers, is broadly new and is applicable to the manufacture of various products other than storage battery separators. Morever, this feature is applicable to other fibers than tree bark to pressure befibers; for example, it can be applied to the sorbing electrolyte and swells sulciently to submanufacture of battery separators, fiber board, stantially ll the space between the plates.

andvarious other products from bagasse, cocoa- From the foregoing description and the acnut fibers, wood fibers, and other vegetable and companying drawing it will now be readily unmineral fibers. 5 derstood that I have provided an improved stor- When a press such as the press` 20 is used for age battery separator which can be economicalthe pressing and drying operation, it may be of ly manufactured from wood bark fibers, such as any suitable construction such as that shown the bers of redwood bark which has heretofore in Fig. 2. As here illustrated, the press may been regarded more or less as waste material. comprise stationary and movable platens 22 l0 Moreover, it can be stated that storage battery and 23 between which a layer or mat 24 of the separators made from tree bark bers have a material is received. Steam or other suitable long life and possess various other desirable heating agent may be supplied to the platens by characteristics.

conduits 22a and 23a. A cylinder 25 incorpo- While I have illustrated and described my imrated in the base of the press is provided with 15 proved battery separator and process, it will be a piston which is connected with the movable understood, of course, that I do not wish to be platen 23 by the piston rod 26 so that when the limited to the particular article herein described piston is actuated hydraulically or otherwise, in detail, but regard my invention as including the platens will subject the material to a desired such changes and modifications as do not conpressure which may be in the neighborhood of 20 stitute a departure from the spirit of -the inven- 500 lbs. per square inch. The thickness of the tion and the scope of the appended claims.

sheet into which the matted material 24 is com- Having thus described my invention, I claim: pressed or molded may be determined by the l. A battery separator comprising a sheet height or thickness of `a suitable mold or mold formed of matted tree bark bers of the type ring 28 in which the material is placed. 1 25 having a relatively high lignin content.

The sheet obtained from the pressing and 2. A battery separator comprising a sheet drying operation is theny trimmed to the size and formed of matted tree bark fibers of the kind shape desired for the battery separator l0 and having a relatively low cellulose content and a the trimmings resulting from this operation are relatively high lignin content.

salvaged and returned to the mixer. 30 3. A battery separator comprising a sheet As an example in the actual production of formed of matted redwood bark fibers. storage battery separators by the above-de- 4. A battery separator formed of matted lcree scribed process, 26 grams of tree bark fibers were bark fibers of the type having a relatively high mixed with 61/2 grams of binder in 100 cubic lignin content andabinder.

Acentimeters of 1%. soap solution, .and when 35 5. A battery separator formed of matted treeA pressed into a sheet produced a battery sepabark fibers of the type having a relatively high rator '7" x 'l" in size and having a thickness on lignin content and an asphalt binder.

the order of .090-to .095". I nd that when a 6. A battery separator comprising a mat separator of these proportions is used in a storformed of lredwood. bark fibers and having y age battery in an available space of .142" be- 40 asphalt incorporated therein as a binder. tween adjacent plates, the material of the separator has an apparent density of .274 after ab- EDWARD FAIRCLOUGH. 

